Ok, it's a 92 flareside I6 2wd, front disc, rear drum. Just recently while driving, seemed everything was fine, then out of no where my brake pedal traveled all the way to the floor. I check fluid and i'm not losing fluid. The odd part is the next stop sign, the brakes worked fine. With engine off the pedal feels like it builds most of it's pressure, with engine on, sporatic operation. Any ideas?

One of your wheel cylinders could be leaking.And if it is bad you probably have air in your system.That would explain it working one minute and not the next.And like jwko said it could be master cylinder.

If it were the power booster the pedal would be hard to push. Betting it's the master cylinder. Had same problem with an 01 Taurus a few years back, occasionally the pedal would go to the floor & no fluid loss. Replaced the MC and has been fine since.

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